The use of thermosetting and thermoplastic polymers or resins to embed or impregnate carbon, aramid, glass, boron and other materials, and mixtures thereof, to prepare prepreg tapes that are subsequently employed to mold various structures and structural components, is known. These prepregs consist of a single ply, continuous sheet having a preselected thickness and a pre-selected width and coiled around a spool as produced similar to the way thin sheet metal is coiled for storage. When later used, the prepreg is sliced to required lengths and widths, stacked or oriented, as required to achieve tailored composite properties, and post fabricated by applying heat and pressure in a conventional manner. The prepreg is presently used to fabricate flat and curved laminated panels as well as structural profiles such as hat-sections, I-beams, T-beams, channels, angles, etc., by conventional molding methods.
Some of the problems encountered in making and using prepreg previously have included the formation of extremely brittle final products and, in the case of thermosetting materials, the inability to reshape or change the final molded material. Pultrusion, a process where fiber filaments are impregnated by being pulled through an immersion bath of suitable thermoplastic or thermosetting polymer, either in solution or in a slurry, is presently employed for making prepreg tape of various widths.
One of the problems found in presently used pultrusion processes is the inability to obtain continuous or long lengths of uniform thicknesses and uniform impregnated prepreg having the desired fiber/resin ratio, which results in numerous splicing of the final product and extra work and time in employing these spliced lengths in fabricating finished articles. Also, this non-uniformity in the prepreg, and the use of spliced prepreg, contributes to the high incidence of voids in final structural components molded from presently available prepreg. Problems in obtaining uniform slurries for insoluble impregnating materials and problems in obtaining complete solubility of soluble impregnating materials are also believed to contribute to non-uniform impregnated fibers that can cause voids in final molded products.